A gap in knowledge remains regarding how specific molecular changes that alter synaptic physiology actuate particular behavioral preferences and memories in living animals. Knowledge on how the cell biology of synapses is altered in the actuation of memories is of critical importance in our aspiration to understand how the building blocks of the nervous system come together to produce its functional output, behaviors. The overall objective of this proposal is to determine how C. elegans synapses between the thermosensory neuron AFD and its only postsynaptic partner (AIY) are modified by experiences to express a learned temperature preference. Our central hypothesis is that temperature preference memory is actuated in AFD through presynaptic plasticity, which is in turn regulated through Protein Kinase C epsilon/eta (nPKC?)-dependent mechanisms. Our hypothesis is based on our preliminary studies and published findings that indicate that altering nPKC? activity in a single neuron (AFD) is sufficient to change the temperature preference of the organism regardless of previous experience. We found that nPKC? localizes near presynaptic sites and alters transmission of AFD sensory information to its postsynaptic partner (AIY). The rationale of the proposed aims is that we can use the compact neural circuitry of C. elegans to dissect how conserved molecules, like nPKC?, regulate presynaptic plasticity to modulate experience-dependent adaptive behaviors. We propose to use genetic, cell biological, pharmacological, behavioral and calcium imaging approaches to achieve our three specific aims: (1) Identify the role of nPKC? in modulating the AFD:AIY chemical synapse; (2) Identify the molecular mechanisms that regulate nPKC? activation; and (3) Identify the presynaptic plasticity mechanism regulated by nPKC?. Upon successful completion of the proposed aims we expect the contribution to be a detailed molecular and cell biological understanding of how the temperature preference memory is actuated in vivo through the regulation of presynaptic plasticity mediated by the conserved nPKC? pathways. The technical and conceptual innovations in this proposal open up new horizons by providing access to the hubs of memory actuation in living animals and with cell biological resolution. We anticipate, because of the molecular conservation of the examined pathways, that advancements in our understanding based on these innovations will result in transposable lessons of broad biological significance.